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Ninja build targets

The Meta/ladybird.py script provides an abstraction over the build targets which are made available by CMake. The following build targets cannot be accessed through the script and have to be used directly by changing the current directory to Build/release and then running ninja <target>:
  • ninja check-style: Runs the same linters the CI does to verify project style on changed files
  • ninja lint-shell-scripts: Checks style of shell scripts in the source tree with shellcheck
  • ninja all_generated: Builds all generated code. Useful for running analysis tools that can use compile_commands.json without a full system build

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CMake build options

There are optional features that can be enabled during compilation for specific types of development work or to introduce experimental features.

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Sanitizers

Sanitizers add runtime checks and may significantly impact performance.
  • ENABLE_ADDRESS_SANITIZER: Builds in runtime checks for memory corruption bugs (like buffer overflows and memory leaks) in Lagom test cases
  • ENABLE_MEMORY_SANITIZER: Enables runtime checks for uninitialized memory accesses in Lagom test cases
  • ENABLE_UNDEFINED_SANITIZER: Builds in runtime checks for undefined behavior (like null pointer dereferences and signed integer overflows) in Lagom and Ladybird
  • UNDEFINED_BEHAVIOR_IS_FATAL: Makes all undefined behavior sanitizer errors non-recoverable. This option reduces the performance overhead of ENABLE_UNDEFINED_SANITIZER

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Fuzzers

  • ENABLE_FUZZERS: Builds fuzzers for various parts of the system
  • ENABLE_FUZZERS_LIBFUZZER: Builds Clang libFuzzer-based fuzzers for various parts of the system
  • ENABLE_FUZZERS_OSSFUZZ: Builds OSS-Fuzz compatible fuzzers for various parts of the system

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Debug options

  • ENABLE_ALL_THE_DEBUG_MACROS: Used for checking whether debug code compiles on CI. This should not be set normally, as it clutters the console output and makes the system run very slowly. Instead, enable only the needed debug macros, as described below
  • ENABLE_COMPILETIME_FORMAT_CHECK: Checks for the validity of std::format-style format string during compilation. Enabled by default
Many parts of the codebase have debug functionality via <component_name>_DEBUG macros, which can be enabled individually at build time. They are listed in Meta/CMake/all_the_debug_macros.cmake.

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Build configuration

  • ENABLE_COMPILER_EXPLORER_BUILD: Skip building non-library entities in Lagom (this only applies to Lagom)
  • LAGOM_TOOLS_ONLY: Skips building libraries, utilities and tests for Lagom. Mostly only useful for cross-compilation
  • LADYBIRD_CACHE_DIR: Sets the location of a shared cache of downloaded files. Should not need to be set manually unless managing a distribution package
  • ENABLE_NETWORK_DOWNLOADS: Allows downloading files from the internet during the build. Default on, turning off enables offline builds. For offline builds, the structure of the LADYBIRD_CACHE_DIR must be set up the way that the build expects

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Testing

  • INCLUDE_WASM_SPEC_TESTS: Downloads and includes the WebAssembly spec testsuite tests. In order to use this option, you will need to install prettier and wasm-tools
  • INCLUDE_FLAC_SPEC_TESTS: Downloads and includes the xiph.org FLAC test suite

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Clang plugins

  • ENABLE_CLANG_PLUGINS: Enables Clang plugins which analyze the code for programming mistakes. See Clang Plugins below

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CMake cache manipulation

CMake caches variables and options in the binary directory. This allows a developer to tailor variables that are set() within the persistent configuration cache. There are three main ways to manipulate the cache:
  1. cmake path/to/binary/dir -DVAR_NAME=Value
  2. ccmake (TUI interface)
  3. cmake-gui
Options can be set via the initial cmake invocation that creates the binary directory to set the initial cache for the binary directory. Once the binary directory exists, any of the three options above can be used to change the value of cache variables.

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Example: Enabling debug macros

Boolean options such as ENABLE_<setting> or <component_name>_DEBUG can be enabled with the value ON and disabled with OFF: 
# Reconfigure an existing binary directory with process debug enabled
cmake -B Build/ladybird -DPROCESS_DEBUG=ON
For more information on how the CMake cache works, see the CMake guide for Running CMake. Additional context is available in the CMake documentation for variables and set().

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Clang-format updates

Some OS distributions don’t ship bleeding-edge clang-format binaries. Below are 2 options to acquire an updated clang-format tool:
1

LLVM apt repositories (Debian-based)

Use the LLVM apt repositories to install the latest release of clang-format.
2

Compile from source

Compile LLVM from source as described in the LLVM documentation here.

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Clangd configuration

Clangd will automatically look for configuration information in files named .clangd in each of the parent directories of the file being edited. The Ladybird source code repository has a top-level .clangd configuration file in the root directory. One of the configuration stanzas in that file specifies the location for a compilation database. Depending on your build configuration (e.g., Debug, default, Sanitizer, etc.), the path to the compilation database in that file may not be correct.
You can use the Meta/configure-clangd.sh script to configure clangd for your build directory.

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Clang plugins

Clang plugins are used to validate the code at compile time. Currently, they are used to detect JavaScript-related garbage collection faux pas, such as neglecting to visit a garbage-collected type.

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Prerequisites

In order to enable Clang plugins, you will need Clang’s development headers installed. For example, on Ubuntu this is the libclang-dev package.

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ccache configuration

When Clang plugins are enabled, it is recommended to have the following environment variable set for ccache: 
export CCACHE_COMPILERCHECK="%compiler% -v"
By default, ccache will include the plugins themselves in file hashes. So if a plugin changes, the hash of every file will change, and you will be stuck with an uncached build. This setting will prevent ccache from using plugins in the file hashes.

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Building the Flatpak

Ladybird has an in-tree Flatpak manifest that can be used to build a Flatpak package for Ladybird. The recommended way to build the Flatpak is to use the flatpak-builder tool.
1

Configure Flatpak

See the Flatpak setup documentation on how to configure your environment for user Flatpak builds, and to configure the Flathub repo.
2

Build the Flatpak

flatpak-builder --user --force-clean --install-deps-from=flathub \
  --ccache --repo=Build/repo --install Build/flatpak \
  Meta/CMake/flatpak/org.ladybird.Ladybird.json
Expect this to take a long time, as it will download and build all the dependencies of Ladybird as well.
3

Run the Flatpak

flatpak run --user org.ladybird.Ladybird

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Debugging the Flatpak

You can pass the --devel and --command=sh flags to flatpak run. This will drop you into a shell in the Flatpak sandbox: 
flatpak run --user --command=sh --devel org.ladybird.Ladybird

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Debugging without optimizations

It’s possible that when trying to inspect certain frame variables in your debugger, you’ll get an error similar to: 
error: Couldn't look up symbols: __ZN2AK6Detail10StringBaseD2Ev
Hint: The expression tried to call a function that is not present in the target, perhaps because it was optimized out by the compiler.
You probably only want to make the build-file change described below while you’re in the middle of examining the state of a particular build in your debugger — and then you’ll want to revert it after you’re done debugging. You otherwise probably don’t want to have the build-file change in place while you’re running WPT tests or in-tree tests and checking the results.

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Disable compiler optimizations

1

Apply the patch

At your command-line prompt in your shell environment, copy and paste the following:
patch -p1 <<EOF
diff --git a/Meta/CMake/lagom_compile_options.cmake b/Meta/CMake/lagom_compile_options.cmake
index 7fec47ac843..45c3af87493 100644
--- a/Meta/CMake/lagom_compile_options.cmake
+++ b/Meta/CMake/lagom_compile_options.cmake
@@ -29,7 +29,7 @@ if (CMAKE_BUILD_TYPE STREQUAL "Debug")
     if (NOT MSVC)
         add_cxx_compile_options(-ggdb3)
     endif()
-    add_cxx_compile_options(-Og)
+    add_cxx_compile_options(-O0)
 elseif (CMAKE_BUILD_TYPE STREQUAL "RelWithDebInfo")
     add_cxx_compile_options(-O2)
     if (NOT MSVC)
EOF
That will patch the build config in such a way as to disable all compiler optimizations and make all debug symbols always available.
2

Tell git to ignore the change

git update-index --skip-worktree Meta/CMake/lagom_compile_options.cmake
This prevents git from considering that build file to have been modified.
3

Rebuild and debug

Run a build again with the Debug preset, and then go back into your debugger. You’ll now be able to inspect any frame variable that you weren’t able to previously.

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Revert the changes

After you’ve finished debugging your code changes with that build: 
git update-index --no-skip-worktree Meta/CMake/lagom_compile_options.cmake \
    && git checkout Meta/CMake/lagom_compile_options.cmake
That will restore your git environment to the state it was in before you patched the build file.

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